The present invention relates to a wire stitching or stapling machine of the type which servers and forms staples from a continuous wire and drives the staples into an associated workpiece. In particular, the invention relates to a stitching head for such a machine.
The present invention is an improvement of the wire stitching machine sold by Interlake, Inc., the assignee of the present invention, under the trademark "CHAMPION STITCHER". This prior stitching machine, which is in turn an improvement of the machine described in U.S. Pat. No. 1,252,011, includes a stitching head having a wire feed mechanism for feeding a predetermined length of wire from a continuous coiled supply to a rotatable wire holder through a cutter which severs the length of wire from the supply, and through a staple-forming and driving mechanism which cooperates with the holder for forming the severed length of wire into a staple and driving it into an associated workpiece against a clincher. The mechanism undergoes a cyclical reciprocating movement comprising a drive stroke and a return stroke. During each drive stroke the feed mechanism feeds a predetermined length of wire to the wire holder, while the staple-forming and driving means is forming and driving the length of wire which had been fed and severed during the preceding drive stroke. Both mechanisms then retract simultaneously, and at the end of each cycle there is left in the wire holder a severed length of wire ready to be formed and driven during the next drive stroke.
When the wire is withdrawn from the supply coil it is not straight, but rather has a certain curvature as a result of manufacturing processes. During each cycle, the wire is severed at the cutter so that, during the next cycle, the leading end of the wire must travel from the cutter to the wire holder which is spaced a predetermined distance from the cutter. While this distance is not great, typically being less than one inch, it is sufficient that the curvature in the uncoiled supply wire will cause the leading end to stray from the feed path and miss the narrow entrance aperture into the holder. Therefore, the prior stitching head includes wire straighteners for removing the curvature from the wire in two different planes before it reaches the gripping and feeding mechanism.
These straighteners comprise pairs of rollers separated by an adjustable cam. The presence of these straighteners makes threading of the wire into the stitching head a complex and exacting procedure. The threading of the wire through the straighteners must be carefully done to insure that the wire is accurately seated in the straighteners. Then, the wire is fed through a check pawl to prevent reverse movement, then through a channel in the cutter and into the entrance aperture of the wire holder. Then a trial and error procedure ensues to obtain the right degree of straightening. Thus, in some applications, the straighteners are first set to a nominal position, the machine is cycled a few times and the wire is cut off just ahead of the cutter. The distance of the free end of the wire from the face plate of the head in a front-to-back direction, and its lateral distance from the center line of the feed path are then manually measured to see if they are within specifications. If they are not, adjustments are made to the straighteners and this process is repeated until an accurate feed is accomplished. As a result, the threading procedure must be done by trained technicians. This is not a serious drawback in some applications, such as in the printing and binding fields, wherein there are long runs of many cycles of stapling standard-thickness workpieces. In such applications there is a commonly a technician permanently on-site.
However, the stitching machine head also has application in office environments, such as in connection with copying machines and the like. In such applications, there is no technician on-site and, therefore, rethreading of the machine, which must be accomplished at least each time the supply coil is exhausted, would require a service call to the technician. The expense of such service calls is a severe disadvantage to the use of the stitching machine head in office applications.